[Evolution of the functional properties of neurons during the process of elaborating a conditioned reflex].

A comparison was made between unit responses of the motor and auditory cortical zones and the parvocellular (auditory) and magnocellular nuclei of the medial geniculate body (MGB) to test presentations of sound and electro-cutaneous stimulation of the limb, both in units recorded before elaboration of conditioned connections and in those recorded in the course of defensive motor conditioning to sound. It has been found that in the course of conditioning, the functional properties of the neurones in the projection structures were changing towards an increase in the number of bimodal cells and a reduction of the number of monomodal cells which respond to a stimulus adequate for the given structure. The number of monomodal cells which in the tests reacted to a non-adequate stimulus became greater. Such changes were not manifested in the magnocellular part of MGB which plays the part of an associative nucleus in the subcortical auditory system.